Structure and mechanical properties of poly( d, l-lactic acid)/poly( ε-caprolactone) blends

A series of blends of the biodegradable polymers poly( d, l-lactic acid) and poly( ε-caprolactone) were prepared by varying mass fraction across the range of compositions. Tensile testing was performed at room temperature using an extensometer and the elastic modulus was calculated for each blend. The blends were also tested to failure, and the strain-at-failure and yield stress recorded. While the blend has been shown to have a lower critical solution temperature, the mechanical properties were insensitive to the annealing conditions. Scanning electron microscopy was used to characterize the blend microstructure and poor adhesion was observed at the interface between blend components. Differential scanning calorimetry was performed but the results were somewhat variable, indicating this blend may have complex phase behavior that depends sensitively on the method of preparation. However, nuclear magnetic resonance data indicate the two components are phase separated. A percolation model is used to explain the observed mechanical data and the results are consistent with the predictions of the Kerner–Uemura–Takayangi model. The results of these experiments demonstrate the utility of polymer blending in tuning material properties.